Patent GB-226265-A (GB)
Title: Improvements in or relating to telephone exchange systems
IPC: H04Q3/62
Filed: 1923-09-11
Abstract: 226,265. Western Electric Co., Ltd., (Deakin, G.). Sept. 11, 1923. Automatic and semi-automatic exchange systems.-The substations of a small private branch exchange are provided with a signal device, such as a lamp, which operates as a dialling signal and may also be used to indicate whether the called line is free or busy. Each substation is also provided with a key which when depressed grounds one of the talking conductors and causes the completion of a circuit for the test relay of the final selector. If the wanted line is free, ringing current is then applied, but if it is busy, the substation signal device is actuated to give a busy signal. In the system described, a local call is set up by an idle connecting unit comprising a line-finder LF and an associated numerical switch FS. The switch FS is a uni-motional switch of the type which takes an initial step immediately it is taken into use, and is then stepped to a wanted line by dialling one or more digits; (the eighteenth contact set is, for example, reached, by dialling the digits 98). The second, third, and fourth, and if desired, further positions, are allotted to outgoing main exchange junctions. These may be engaged in succession by repeatedly dialling the digit 1, and are tested by depressing the substation testing key 25. Provision is made whereby some substations are prohibited from making main exchange calls. Main exchange calls may be made by the P.B.X. operator, who also deals with incoming calls from the main exchange. Call to another P.B.X. subscriber. On the calling subscriber removing, his receiver 1, a circuit is closed for a group starting relay 2 and the signal lamp 5, but owing to the inclusion of the series resistance 3, the lamp 5 does not glow. The relay 2 closes a circuit for the starting relay 8 of the line-finder LF of the first idle connecting circuit, and the stepping magnet 12 is energized in a self-interrupting circuit to rotate the wipers 20, 21, 18, 15, 55, 45. When the calling line is engaged, the test relay 13 energizes in series with the lamp 5 over the wiper 15, opens the circuit of the stepping magnet 12, and energizes a switching relay 17, which completes a circuit over the calling loop for both windings of the relays 22, 23. The relay 22 is differentially wound and does not respond, but the relay 23 pulls up and closes a circuit over the connector wiper 27 in its normal first position, for the magnet 26. which drives the connector FS into its second position, where the starting wire from the relay 2 is extended over the strip contact 30 to the next connecting circuit. The relay 8 is also de-energized at wiper 10, and removes a shunt from the left-hand winding of the cut-off relav 4, which energizes in series with the lamp 5 in a locking circuit of the relay 13 extending over a second test wiper 18, and by removing a shunt from its own high-resistance right-hand winding marks the calling line busy. The lamp 5, when energized in series with the test relay 13, glows and indicates to the calling subscriber that he may commence dialling the wanted number, which may comprise one or two digits. At each impulse the relay 23 relapses and closes a circuit over both its armatures for the stepping magnet 26, which rotates the connector wipers to engage the wanted line contacts. The magnet 26 is energized during the full period of each relapse of the line relav 23, thus preventing any possibility of overstepping. In a modification for ensuring the operation of the stepping magnet 26 if the dialling breaks are short, a lowresistance quick-acting relay 32 is inserted in series with the magnet 26. This relay 32 responds directly the stepping circuit is closed, and completes an independent locking circuit (for itself and the stepping magnet) which is effective until the stepping magnet has attracted its armature sufficiently to step on the switch. To test the wanted line, the calling party momentarily depresses the key 25, thereby grounding the lower talking conductor and causing the response of the differential relay 22, which completes a circuit for the left-hand winding of the test relay 35. If the wanted line is busy the test relay 35 remains deenergized, the line-finder wiper 45 is earthed, and the lamp 5 is short-circuited. Assuming the called line is free, the test relay 35 pulls up and locks up over its right-hand winding in series with the wanted line cut-off relay. The test relay 35 also completes a circuit over wiper 37 for a ring- ing relay 40, which prepares a circuit for the ringing cut-off relay 39, energizes the relay 43 of the ringing mechanism, and connects the ringing lead to the upper talking conductor. The relay 43 operates to transmit intermittent ringing current over the called line as described in Specification 208,073, [Class 38 (v), Electric switches &c.], until the called party answers and the cutoff relay 39 is energized to disconnect the ringing relay 40, and complete the talking circuit. When the calling subscriber hangs up, the relays 4, 13, 23, 17 de-energize and a restoring circuit is closed for the stepping magnet 26 over the wiper 27. The relay 39 relapses when the called party hangs up. A key 11 is provided whereby if a fault develops the line-finder LF and connector FS may be cut out and the starting circuit extended to the next connecting unit. Outgoing call to a junction line 50, 51. When the P.B.X. party removes his receiver his line is extended over a line-finder LF to a connector FS which steps to its second position as in the case of a local call. The calling party then depresses his key 25 to test the first junction line, which terminates in this position. If this junction is busy, the lamp 5 is extinguished as before, and the calling party dials the digit 1 to advance the connector to the next junction line which is tested in like manner. Assuming the junction 50, 51 is the first idle one, the test relay 35 energizes in series with the junction cut-off relay 53, and closes a circuit over brush 37 for the relay 14, which de-energizes the relay 17 and completes a clean metallic circuit to the junction 50, 51. The cut-off relay 53 energizes a relay 54, which disconnects the operator's apparatus OP, OTS, and connects the junction through to the main exchange. If it is desired that a P.B.X. subscriber should not have facilities for calling the main exchange, the wire 70 is disconnected from the bank terminal 56 to prevent the energization of the switching relay 14. Incoming call from main exchange. On hearing the bell 57, the tone of which indicates the calling junction, the operator throws the answering key 60. which removes battery from the junction test wire to mark the junction busy, and energizes a relay 61. The relay 61 locks up, connects a holding retardation coil 63 across the junction, and lights a guard lamp 64. The operator now enquires the number of the wanted P.B.X. line, restores the answering key 60, throws a local line key 65, obtains connection with the wanted party by dialling his number, and tells him which junction to call. The connection between the P.B.X. party and the operator is then released, and the former obtains a connection with the main exchange junction as described in the previous para. graph. The relay 53 then energizes, and de-energizes the relay 61, which extinguishes the guard lamp 64 and disconnects the retardation coil 63. Main exchange call established by P.B.X. operator. The operator throws the answering key 60, and the release key 62 of an idle outgoing junction, thereby marking the junction busy by removing battery from the test wire, and connecting the operator's set OTS across the junction. The operator then dials to actuate the automatic apparatus at the main exchange. To transfer the call to a P.B.X. subscriber, the key 62 is restored, whereupon the relay 61 energizes and places the holding coil 63 across the junction, while the operator calls the P.B.X. subscriber and tells him to call the junction as described in the previous paragraph. The Provisional Specification also describes a modified system in which each substation is provided with a three-position ringing and testing key 13, Fig. 1 (Prov.), mechanically interconnected with the switch-hook and with a tripping lever 24. On a P.B.X. subscriber removing his receiver to make a call, an idle line-finder LF is set in operation, and when the calling line is found, the signal lamp 25 glows and gives a dialling signal. On the completion of dialling, the calling subscriber operates key 13 to its third position in which all the contacts are operated, and the test relay 27 is brought into circuit. If the wanted line is free, ringing current is connected up, some also being sent back to the calling subscriber over a third winding 41 of the substation induction coil 45. The calling party then releases the key 13 to an intermediate position in which the contacts 43, 44 and 14, 15 only are closed. When the receiver is replaced, the switch-hook unlocks the key 13, which returns to its first position and causes the release of the automatic switching apparatus. Each main exchange junction, such as JC, has a common conductor 55 multipled to a junction busy signal 54 at each P.B.X. station. To call a junction line. the subscriber removes his receiver and after receiving the dialling signal, moves the key 13 to its third position to test the first junction line. If this is busy the test relay 27 does not energize, and ground on the test wiper 34 completes a stepping circuit for the magnet 28. This operation continues until an idle junction is found. Assuming the junction JC is idle, its cut-off relay 59 is energized, and a circuit is closed over relays 57, 56 and the common conductor 55 for the signal relay 54, which locks up over its low-resistance winding (causing the response of marginal relay 57), and indicates which